Carburetor and method of carburation

ABSTRACT

An improved carburetor and method of carburetion employs an elongated, flexible reed within the air passage of a carburetor to eliminate the conventional fixed venturi and throttle shaft from the air passage, to function as a variable venturi, to regulate the air flow, and to prevent reversion of a mixture of air and fuel into the upstream portion of the air passage of the engine.

v United States Patent [191 3,917,7 2 Nov. 4, 1975 Herbrandson llllll2,148,071 2/1939 lrgens....,....,-................. 2,455,775 12/1948Johnston et a1........

[ CARBURETOR AND METHOD OF CARBURATION [76] Inventor:

2,779,576 1/1957 Morgenroth 3,042,013 3,046,958

Bard et a1. Schneider n o k e N 2 6 9 n. 7

Dale Herbrandson, 1605 Lynngrove Drive, Manhattan Beach, Calif. 902663,361,120 3,680,846 8/1972 Bickhaus et a1.

[22] Filed: Mar. 19, 1974 Primary Examiner-Tim R. Miles [21] Appl. No.:452,654

Attorney, Agent, or FirmBurns, Doane, Swecker & Mathis [52] US. Cl.261/62; 123/73 A; 123/73 V; 261/DIG. 68

7] ABSTRACT 52 An improved carburetor and method of carburetion employsan elongated, flexible reed within the air passage of a carburetor toeliminate the conventional fixed venturi and throttle shaft from the airpassage, to function as a variable venturi, to regulate the air flow,and to preventreversion of a mixture of air and fuel 261/62 into theupstream portion of the air passage of the en- 261/62 gim 123/73 A261/62 7 Claims, 3 Drawing Figures [51] Int. FOZM 9/10 [58] Field of123/73 V, 73 A,

261/62, DIG. 68

[56] References Cited UNITED STATES PATENTS 1,552,623 9/1925 Little1,624,024 4/1927 Svensson et a1.

1,625 ,787 4/1927 Braselton US. Patent Nov. 4, 1975 Sheet 1 of23,917,762

U.S. Patent Nov. 4, 1975 Sheet 2 of2 3,917,762

CARBURETOR AND METHOD OF CARBURATION BACKGROUND OF THE INVENTION Thisinvention relates generally to an improved carburetor and method ofcarburetion for an internal combustion engine. More specifically, theinvention relates to an improvement of a carburetor for a two-cycleinternal combustion engine in which a flexible, elongated reed functionsin conjunction with a variable stop to control the quantity of air andfuel admitted to the combustion chamber of the engine, whileconcurrently serving as a variable venturi and protecting orificesthrough which fuel enters the carburetor from pressure developed in thecrankcase of the engine.

Many two-stroke engines use a reed valve in series with a carburetor tomeet the induction requirements of the engine. In a chain saw, forexample, a typical installation mounts the reed valve assembly directlyto an adapter on the crankcase. The carburetor is placed upstream fromand adjacent to the reed valve. The carburetor functions to form thedesired mixture of air and fuel, and to regulate the engine output byproviding a means to regulate the air flow. The conventional r'eed valvefunctions as a check valve allowing the mixture of air and fuel to enterthe crankcase, but not to escape. The reed valve is sensitive to theengine air flow demand and does not have fixed timing such as would befound with a cam actuated poppet valve, a piston timed valve, or arotary valve.

Although the conventional arrangement gives generally acceptable engineoperation, there are several areas which could be improved. For example,the conventional carburetor and reed assembly in series requiresconsiderable space. In a chain saw which is carried and operatedmanually, space means undesirable weight. On a motorcycle, the length ofthe series arrangement can create a problem in fitting the air filterassociated with the carburetor within the space available. I

The venturi in the conventional carburetor must create a pressure dropto operate. Usually the constricted air passage comprising the venturiis sized only for stable operation in the mid-range of the engine powerband. Such a venturi may thus be too small for optimal power at highengine speed, and too big to create the desired pressure drop at verylow engine speed. A variable venturi could solve this problem.

The conventional air intake passage often may be cluttered. There arethree principal restrictions in the air stream of the conventionalcarburetor and reed installation, viz., the venturi, the throttleshutter and shaft, and the reed valve assembly. Each of theseremaintains a contoured surface in contact with the petstrictions, whenplaced in series, will account for a portion of the pressure loss acrossthe intake system, and

the conventional series placement of the carburetor and reed may requireall three restrictions to be in the air stream for proper operation ofthe engine. The improved carburetor, as will be discussed further on,can eliminate the first two restrictions from the air stream and alsooffer a more compact assembly. This is accomplished by combining thefunctions of the throttle, venturi, and reed valve by a unique design.The improved carburetor operates without a conventional throttle shutteror venturi in the air passage.

The throttling requirements in the reed carburetor are met bycontrolling the lift of the reed petals by use of a movable reed stop.At wide open throttle the movals. During idling, the contouredstop-throttle presses the longitudinal midpoint of the reed against thecarbu- 0 retor body while allowing a slight movement of the petal tipsfrom normally closed positions. This movement allows the idling air topass at relatively high speed over the idling fuel passages under thetips of the petals.

The improved carburetor optimally operates without a conventionalventuri upstream from'the reed petals. The venturi in the reedcarburetor is located at the V-shaped portion of the air passage formedbetween the lifting or vibrating tips of the reed petals and thecarburetor body. The air flow accelerates in the V- shaped region,reaching its'maximum velocity near the tips of the reed petals. Theincreased air velocity is accompanied by a reduction in air pressure.The pressure differential aspirates the fuel into the high velocity airstream through orifices disposed adjacent to the tips of the reedpetals; Since there are no restrictions upstream from ,the petals, theentire pressure differential in the carburetor throat occurs across thereed petals. When engine air demand decreases due to reduced enginespeed under load, the reed does not use all of the available lift eventhough the variable reed stop is in the wide open position. Thisdiminished lift results in a reduced venturiat the tip of the reed. Thereduced area tends to maintain a high velocity across the orifices,maintaining good aspiration of fuel into the air stream.

Many carburetors appearing in the prior art may fail to provideeffective admission of fuel to the throat of the carburetor when thethrottle is closed and the associated engine is idling at low speed.While fuel is admitted to the throat of the carburetor by aspirationwithin the venturi during operation of the engine at high speed, whenthe engine is idling, fuel may be drawn into the throat of thecarburetor only by a relatively high suction head-developed by theengine downstream from the closed throttle shutter. Since the throttleis closed during idling, the port which is exposed to suction must belocated downstream from the shutter. Usually a second port is providedto admit bleed air from the upstream side of the closed shutter to thefuel circuit supplying fuel during idling. This arrangement allows anemulsion of air and fuel to be formed incident to the direct suction ofthe engine. The emulsion is then mixed with the air passing one side ofthe closed throttle shutter which is cracked open. The other side of theshutter normally provides only a leakage of air. The same conditionsgenerally continue to prevail as the conventional carburetor is operatedat a speed just above idling.

In contrast, the reed carburetor passes all of the air flow over fuelorifices during idling, part throttle, and full throttle. As a result,no leakage occurs as in the conventional carburetor using a throttleshutter and shaft and the fuel may be more efficiently atomized andmixed with the air entering the engine.

Somewhat related to the problem of ineffective induction of fuel intothe throat of a carburetor during idling is the problem of maintainingan adequate velocity head within the venturi for efficient aspiration offuel when the throttle of the carburetor is fully open and the engine isoperating under load at less than full speed. Those skilled in the artwill appreciate that air flow will be reduced under these luggingconditions. In conventional carburetors the venturi may be comprisedsimply of an annular constriction in the air passage. The constrictionis fixed in size and serves to increase the velocity of air flowingthrough the throat of the carburetor. The resultant increased velocityresults in a pressure drop which aspirates fuel from a port disposed inthe constricted area of the throat of the carburetor. As the engineslows under a load, the demand for air may decrease linearly and as aresult, the volume of air flowing through the venturi may decrease in alinear fashion. However, while the velocity and volume decreaselinearly, the pressure drop across the venturi varies with the square ofthe air velocity. As engine speed drops and the air velocity decreases,the venturi rapidly becomes unable to aspirate the fuel, and the enginemay falter from a too lean mixture. The conventional carburetorapproaches this velocity problem by sizing the venturi for stable engineoperation at medium values of rpm, and accepting a loss of availablepower if the flow of air goes sonic, i.e., if the venturi becomes chokedat high engine speed. It would therefore be highly desirable if aventuri could be provided which would be variable and which wouldthereby maintain a velocity head of sufficient magnitude to provide foreffective aspiration of fuel for all practical values of engine air flowrequirements.

Many carburetors of the prior art are not suitable for use in randompositions. For instance, many carburetors of the prior art may notfunction properly when inverted or when rotated in one or moredirections. Such carburetors would not be suitable for use in a tool orother environment in which the engine must operate in a variety oforientations. As suggested by the previous discussion, many carburetorsof the prior art may entail separate fuel circuits for the introductionof fuel during idling and during operation of the engine at high speeds.As indicated, the orifices which introduce the fuel during these twophases of operation may open into the throat of the carburetor somedistance from one another. Because of the separation of the orificesrelative to one another and because of the tendency of the fuel to seeka single horizontal level, if one circuit and orifice is elevated abovethe other, fuel may drain away from the elevated orifice and may therebyprevent effective induction of fuel into the throat of the carburetor.This problem may be made more difficult by carburetors of the prior artwhich employ a throttle shutter of the type commonly referred to as abutterfly valve. These engines may depend upon a pressure differentialcreated across the closed throttle shutter by the suction of the engineto directly suck fuel from an idling fuel orifice or port locatedimmediately downstream from the closed edge of the throttle shutter.Since free movement of the butterfly valve may be obstructed by theconstriction which forms the venturi, the valve and thus the idling fuelport must of necessity be located a considerable distance downstreamfrom the venturi and the main fuel port. It would, therefore, be quitedesirable if a carburetor could be provided in which the idle and themain fuel orifices are disposed in close spatial relation to one anotherin order to minimize elevational differences incident to variousorientations of the carburetor.

Many engines of the prior art employ flexible reed valves as checkvalves downstream from the carburetor to prevent reversion, i.e., theintroduction of back pressure from the crankcase of the engine into thethroat of the carburetor. The cyclic negative pressure or suctiondeveloped in the crankcase of a two-cycle engine is relied upon to drawair through the throat of the carburetor. However, if the throat of thecarburetor were exposed to the cyclic positive pressure developed withinthe crankcase, the positive pressure could purge the orifices of fueland prevent proper operation of the carburetor. Therefore, a check valveshould be provided for such engines which will allow the flow of airthrough the throat of the carburetor and into the crankcase of theengine when the pressure of the crankcase is negative and which willisolate the fuel orifices from back pressure which may be developed whenthe pressure in the crankcase is positive.

Many engines of the prior art provide such valves immediately adjacentthe crankcase and these valves may therefore be exposed to ratherintense heat and air turbulence from the rotating crankshaft. Exposuremay cause oxidation, weakening, or other damage to the valve,particularly if the valve is an epoxy fiberglass composite generallyused for this purpose. It would thus be desirable if a carburetor couldbe provided in which a valve, which would open and close in response tothe negative and positive pressures, respectively, of the crankcase, islocated at a position away from the areas of the engine generating heatand air turbulence so that damage to the valve may be avoided.

Many carburetors of the prior art used in conjunction with a reed valvemay present the problem of the two units in series being larger thandesired for use with an engine employed in a particular environment. Forinstance, if the engine is to be employed in a chain saw, it must becovered with a protective shroud and the entire assembly must be smallenough to allow use in relatively restricted areas. Also, when the toolmust be handled manually, the weight of the tool is a majorconsideration and every saving which can be made in weight is important.If an engine is to be used to power a motor-cycle it must fit within arather small structural framework. An unnecessary protrusion, such asthat which may occur if the air intake system is excessively long, mustbe avoided in order to use efficiently the space available for theengine and associated hardware. In many reed valve applications of theprior art a considerable portion of the length of the induction systemis taken up by the space required to place the reed valve and associatedconnective structure between the carburetor and the engine. Therefore,it would be highly desirable if a carburetor could be provided in whichthe reed valve assembly is simply included within the length of thecarburetor, for a substantial savings in size of the assembly.

Other carburetors of the prior art which employ conventional venturismay be subject to the problem that when the engine is operating near itsmaximum power the flow of air through the venturi may go sonic. That is,the flow of air may reach a velocity which simply cannot be increased,regardless of the demand of the engine, and the venturi is said to bechoked. A choked venturi limits engine output because the volume ofcombustible mixture delivered to the engine is proportional to the airvelocity through the carburetor venturi. It would, therefore, be highlydesirable if a carburetor could be provided which avoids the phenomenonof the air passing through the venturi reaching a maximum velocitybefore the engine reaches its air intake limit.

OBJECTS AND SUMMARY OF THE PREFERRED FORMS OF THE INVENTION Objects Inlight of the foregoing it is therefore a general object of theinventionto provide an improved carburetor and method of carburetion intended toobviate or minimize the problems of the type previously noted.

It is a particular object of the invention to provide an improvedcarburetor and method of carburetion wherein the venturi varies inresponse to the demand of the engine to maintain the velocity of airpassing through the venturi needed to effectively aspirate fuel from amain fuel port disposed therein.

It is another object of the invention to provide an improved carburetorin which the orifices, through which fuel is admitted to the throat ofthe carburetor during both idling and operation at high, speeds, arelocated in close proximity to one another and in a location close to thecenter of the fuel reservoir so that both orifices will experience onlya small change in the static head of the fuel regardless of the positionin which the unit is operating.

It is yet another object of the invention to provide an improvedcarburetor and method of carburetion in which fuel is introduced duringidling by aspiration from a fuel port into the carburetor incident tothe passage of air through a venturi in which the port is disposed.

It is still another object of the invention to provide an improvedcarburetor in which a valve, which allows the flow of air and fuel intothe engine and which isolates the fuel ports from any positive pressuredeveloped by the engine, is located away from areas of high temperatureand turbulence to at least partially avoid oxidation, weakening, orother damage to the valve.

It is a further object of the invention to provide an improvedcarburetor incorporating the desirable operating characteristics of aseries reed valve, but which is compact and therefore suited to use withan engine employed to power chain saws, motorcycles, or other devices inwhich only a limited amount of space is'available for the engine andassociated hardward.

It is still a further object of the invention to provide an improvedcarburetor and method of carburetion in which the volume of the airpassing through the carbu retor does not reach a premature maximumbefore the air intake limits of the engine are reached at high speed,without compromising the ability of the carburetor to form the correctair/fuel ratio needed to effectively operate the engine at lower .valuesof engine speed.

Brief Summary An improved carburetor according to a preferred embodimentof the invention intended to accomplish at least some of the foregoingobjects includes an air ini the correct mixture of air and fuel. Aflexible elongated reed is cantilevered across the air passage andfunctionsas. a reed check valve to prevent reversion of the mixture ofair and fuel, and also to throttle the air flow. The reed may be movedfrom its normally closed position to a variably open position by thedecreased pressure caused by the engine inducting air through thecarburetor air passage. When air flows past the tip of the reed petals,a pressure drop is created by the increased air velocity, whichaspirates fuel into the airstream from passages located at the tip ofthe reed petals. The extent to whichthe reed may open is controlled by aregulating'device which may be employed to selectively limit the lift ofthe reed to regulate the quantity of air and fuel entering the engine.Thus, the reed valve may be employed to concurrently control thequantity of fuel and airadmitted to the engine and to isolate the fuelorifices withinthe carburetor from any positive pressure developed bythe engine incident to reversion.

An improved method of carburetion according to the I present inventionmixes fuel and air and introduces this mixture into an internalcombustion engine. This induction is accomplished by the proper use ofthe cyclic positive and negative pressures within the crankcase of theengine created by the reciprocating piston. Fuel is introduced into acarburetor connected to the engine in response to these cyclicalpressures. Air and fuel are introduced into the interior of the airpassage of the carburetor in response to the negative pressures and aremixed therein ,as the air flows through the air passage into the engine.The orifices through which the fuel enters the air passage are isolatedfrom the positive pressures by closing a reed valve disposed in thecarburetor and normally closing the air passage in response to positivepressures. The orifices are exposed to the negative pressures when thereed valve opens in response to the negative pressures. The quantity offuel and air entering the engine and the power output thereof arecontrolled by regulating the degree to which the reed valve opens. I

THE DRAWINGS Other objects and advantages of the present invention willbecome apparent from the detailed description which follows consideredin conjunction with the accompanying drawings wherein:

FIG. 1 is a perspective view of an embodiment of the invention shown inposition on a typical small internal combustion engine; i v

FIG. 2 is a transverse sectional view of an embodiment of the inventiontaken along the lines 2-2 of FIG. 1 showing the improvement of thesubject inventionas applied to a typical carburetor; and

FIG. 3 -is an exploded perspective view of a portion of the improvedcarburetor according to a preferred embodiment of the invention.

into reservoirs adjacent the interior of the air passage 16 by means ofthe pump 20. The manner in which this is accomplished will be describedin more detail in connection with the discussion of FIG. 2. A throttleis disposed in the carburetor and is operated by means of a throttlelever 22 and associated pivot pin 24. The function of the throttle willalso be hereinafter more fully described. The carburetor is secured tothe engine by means of a throttle support plate 26 which is secured tothe carburetor and an insulating base plate 28 which is secured both tothe support plate 26 and the engine 10.

As illustrated, the carburetor is located so that the throat 16 opensdirectly into the crankcase 32 of the engine. A valve located in thisarea and employed to isolate the carburetor from the interior of thecrankcase may therefore be subject to damage by heat and turbulencedeveloped in this area. This potential is neutralized by the uniqueplacement of the valve as will be more fully described in connectionwith FIG. 2.

It will be noted that the truncated nature of the throat 16 of thecarburetor allows the carburetor to occupy less space and to be orientedin a manner which reduces the degree to which the carburetor protrudesfrom the engine. As suggested in the preceeding, the compactness of thisarrangement renders the carburetor more suitable for use with enginesoperating within closely confined areas. In particular, such anarrangement may render the improved carburetor more advantageous for usein a chain saw, motorcycle, or other engine powered device.

FIG. 2 illustrates a transverse sectional view of an embodiment of theinvention taken along lines 22 of FIG. 1. It should be noted at theoutset that the particular type of carburetor to which the improvementis applied was chosen only as exemplary of a typical carburetor andshould not be construed as a limitation upon the applicability of theimprovementto other types of carburetors. The invention, for instance,could equally well be applied to those carburetors commonly. referred toas float carburetors.

While the particular structural characteristics of thecarburetorillustrated are not in themselves significant, it may be helpful to afull understanding of the improvement according to the present inventionif the function of the carburetor is briefly described. In thisconnection and as illustrated, a fuel hose 18 admits fuel throughconduit 36 to an annular filter 37 which feeds to a temporary reservoir38 from which the filtered fuel is drawn through conduit 40 andassociated check valve 44 into a pump chamber 42. The fuel is drawn fromthe reservoir 38 into the pump chamber 42 by the suction effect createdin the pump chamber 42 by the displacement of a pump diaphragm 46downward. The diaphragm 46 moves downward, away from the pump chamber42, in response to suction introduced to chamber 43 through conduit 48from the crankcase of the engine. Once fuel is drawn into the pumpchamber 42, the check valve 44 closes.

The suction introduced through conduit 48 to cham- 8 in use, the mainand idle fuel reservoirs may be interconnected or merged into a singlecentral reservoir which contains all of the fuel used both during idlingand high speed operation. It should be appreciated in this regard thatonly the particular configuration of the reservoirs illustrated in FIG.2 would be altered in such carburetors. The main and idle fuel circuitrywould remain essentially unchanged.

As indicated in connection with the earlier discussion of FIG. 1, thecarburetor 8 shown in FIG. 2 is connected to, the engine through thethrottle support plate 26 by means of the insulating base plate 28.Within the body of the carburetor 12, upstream from the throttle supportplate 26 and away from the crankcase 32 (see h FIG. 1), is disposed aflexible, elongated reed 64. The reed 64 is secured to a seating meansor surface 90 on body 12 by means of threaded fasteners 66 and a formedclamp 68. The configuration andsequential arrangement of these elementscan perhaps best be seen in the explodedperspective view shown in FIG.3. The flexible, elongated reed 64 is cantilevered across the truncatedthroat or air passage 16 of the'carburetor and normally closes the airpassage. The flexible elongated reed 64 therefore isolates the airpassage 16 into an upstream portion 74 and a downstream portion 76. Thisserves to protect fuel orifices disposed in the upstream portion of theair passage from the crankcase pressure developed by the engine in thedownstream portion.

The reed 64 has been moved to a position within the body of thecarburetor away from the engine crankcase 32. At such a location thevalve is less subject to. the high temperatures, or turbulence developedwithin the crankcase tending to cause oxidation, weakening, or otherdamage to the reed.

In extending across the air passage 16, the tip 70 of the reed directlyseals an idling fuel port or orifice 72 through which fuel is conductedfrom the idling fuel circuit '62 into the downstream portions 76 of theair passage 16. Thus, in this closed posture the'reed 64 not onlyisolates the upstream portion 74 of the air passage 16 from'pres'sures''which may develop in the ,downstream portion 76, but the tip alsodirectly seals the I idling port to ensure that this port is notsubjectedto ber 43 is followed by a period of positive pressure in whichthe pump diaphragm 46 is displaced upward. The fuel contained in pumpchamber 42 is thereby forced through a second check valve 50 intoconduit 52 and ultimately into a primary fuel reservoir 54. From thereservoir 54 the fuel can enter either a main fuel reservoir 56 or anidling fuel reservoir 58 through variable orifices 55 and 57,respectively. From the main fuel reservoir 56, fuel can enter main fuelcircuitry 60. Similarly, fuel from the idling fuel reservoir can enteran idling fuel circuit 62. In some carburetors presently any pressuresufficient to purge the orifice or. circuit of fuel. 1

The fuel from the main fuel reservoir passes through the mainfuelcircuitry 60 and enters the air passage 16 through main ports ororifices 82. FIGS. 2 and 3 illustrate that-the main ports 82are-disposedin very close relation to the idle port 72, and that there are provideddual, laterally opposed sets of orifices. This arrangement of dual setsof orifices will be more fully described in subsequent discussion. Thevery close proximity between the idle port and the main port ensuresthat, regardless of the position of the carburetor, the elevation headof the orifices will be very nearly the same. This will minimize thetendency of fuel to drain away from either orifice. By minimizing thedifference in elevation head and the possibility of fuel draining fromone of the orifices, more effective operation of the fuel inductionprocess may be insured in an all position application.

The downstream portion of the idling fuel circuit is bifurcated and isin this regard characterized by a branch 78, through which fuel foridling enters the downstream air passage 76, and a branch 80, throughwhich bleed air from the upstream air passage 74 may enter duringidling. The second branch also may serve as a fuel passage during thetransition from idling to higher speeds of operation. The operation ofthe second branch will hereinafter be more fully described. A secondbleed air passage 84 is provided to introduce air into fuel being drawnthrough the main fuel circuitry 60. It has been found that theintroduction of bleed air into the main fuel circuit provides a morecrisp throttle response. That is, when the throttle is opened, theresponse of the engine is more immediate.

It will be appreciated that the provision of bleed air may enhance theinduction of fuel into the air passage 16 from either the main or theidling fuel circuits by virtue of the tendency of the bleed air to forman emulsion with the fuel prior to induction into the air passage. Thus,the fuel may already be partially aerated before it is aspirated intothe air passage and atomization within the air passage may therefore bemore complete. If the fuel is partially emulsified prior to aspirationand if the aspiration is thus rendered more effective, the fuel and airmixture may comprise a lighter mass which will be more easilyaccelerated into the air stream.

A check valve 59 is placed between main fuel reservoir 56 and thejunction of passages 84 and 60. This prevents the emulsified mixture offuel and air from being forced back into reservoir 56 in the event 'thethrottle is snapped shut while there is a high velocity flow of air inthe air passage 16.

The quantity of the bleed air which will be introduced into either themain fuel circuit or the idle fuel circuit can be adjusted by varyingthe diameter and/or the length of the bleed air passage to increase ordecrease the head loss experienced by the air in passing through thepassages. Also, the farther the opening 85 of the bleed air passage 84is located from the orifices 82, the greater the pressure differentialwill be between the main fuel orifice 82 and the opening 85 of the bleedair passage 84 due to the increased air velocity approaching the tip ofthe reed in the air passage 74. The greater the pressure differential,the greater will be the quantity of air drawn through the bleed airpassage. A non-linear amount of bleed air may be introduced into themain fuel orifice 82 by proper placement of orifice 84 in the upstreamair passage 74.

As indicated in connection with the discussion of FIG. 1, the air flowthrough a carburetor improved according to the present invention can becontrolled by means of a throttle lever 22 and an associated pivot pin24. As illustrated in FIG. 2 a regulating means or stopthrottle 86,which controls the lift of reed 64 is secured to the pivot pin 24. FIG.3 presents an exploded perspective view of the stop-throttle, pivot pin,and lever assembly and should be referred to for a more completeunderstanding of the configuration and arrangement of these elements.Rotation of the throttle lever 22 rotates the pivot pin 24 and moves thestop-throttle 86 relative to the air passage 16 to alter the position ofthe reed 64.

When the engine is idling, only a small amount of air and fuel isrequired and the throttle lever and pivot pin are moved to position thestop-throttle 86 to hold the reed 64 in the position shown in solidlines. The tip 70 of the reed, however, is free to vibrate from theposition shown in solid lines to generally the position shown in brokenlines at A. In other words as the engine cyclically develops a negativeintake pressure, air is drawn from the upstream portions 74 of the airpassage 16 past the reed 64 to displace the tip 70 of the reed to theposition illustratedby the broken lines at A. Only a small opening iscreated by the displacement of the reed and the air moves past the idlejet 72 at a relatively high velocity, aspir'ating fuel fromthe orifice72. The velocity of the air passing the idle jet 72 develops by reasonof the small aperture or venturi formed between a venturi surface 88surrounding the fuel ports and the tip of the reed. This aspirationshould not be confused with the direct suction employed by certaincarburetors of the prior art to draw fuel into the air passage.Aspiration through the venturi may afford more effective atomization ofthe fuel than does direct suction. As the pressure within the crankcasecyclically reaches a zero value, the tip of the reed moves back to theposition shown by the solid lines, thereby directly sealing the orifice72. Therefore, when a positive pressure is cyclically developed withinthe crankcase, the orifice 72 has been directly sealed and the main fueljet 82 and the transition fuel passage are isolated from the positivepressure.

When the engine is operating under load at full throttle, thestop-throttle 86 is located in the position shown by the broken lines atC while the reed 64 vibrates between the position shown by the solidlines and a position of generally more extreme flexure as indicated bythe broken lines at B. When the engine is functioning in this manner,the stop-throttle does not contact the reed, instead the reed flexes toa variably open position dependent upon. the quantity of air flowingthrough the air passage 16 in response to the demand of the engine. Thevariably open position of the reed forms a variable venturi between thetip of the reed 70 and the venturi surface 88 which maintains thevelocity head of the air passing through this variable venturi in directproportion to the flexural stiffness of the reed. In other words, thestiffer the reed, the greater will be the velocity head for a givendemand by the engine. This relation will continue until the enginereaches top speed, when the reed will vibrate between the position shownin solid lines and that shown by the broken lines at C. Contact with theretracted stop-throttle 86 in position C preempts the proportionalrelation. The relation may also be preempted by movement of thestop-throttle into contact with the reed.

With the velocity head dependent upon the flexural stiffness of thereed, the velocity should remain relatively constant and the requisiteamount of fuel should be effectively aspirated into the downstreamportion 76 of the air passage 16 while the engine operates under load atfull throttle. It will be recalled from the earlier discussion that aconstant area venturi does not provide this advantage. In thecarburetors of the prior art, if the engine lugs down or decreases inspeed due to loading, a smaller quantity of air flows through theventuri with the result that the velocity head decreases and less fuelmay be aspirated into the air passage. With a carburetor improvedaccording to the present invention, an adequate quantity of fuel will beaspirated into the air passage even though the demand for air by theengine decreases.

It will be recalled from the earlier discussion of the bleed aircircuitry that the branch 80 of the idling fuel circuit was described asadmitting bleed air during idling and as a fuel passage duringtransition by the engine from idling to higher speeds. With regard tothe latter function, this branch will be useful as the reed moves fromthe position shown generally at A to that shown generally at B or C. Asthe reed moves more toward a position at B, the narrowest portion of theopening or venturi formed between the tip 70 of the reed and the venturisurface 88 moves slightly upstream from its original position near theidling fuel port 72. As this movement occurs, the venturi may becomeless effective with regard to aspirating fuel from the idling fuel port72. Furthermore, until the engine begins operating at higher speeds, thevelocity head may not be of sufficient magnitude to effectively aspiratefuel from the main fuel ports located slightly farther upstream.Therefore, an intermediate port is provided in the form of thetransition port 80 so that fuel may be progressively aspirated from theidling fuel port, the transition port, and ultimately the main ports asthe speed of the engine increases.

Whenever it is desired to control the speed with which the engineoperates, the stop-throttle 86 may simply be rotated to a desiredposition within the range defined by the solid and broken linerepresentations to contact and partially close the vibrating reed 64.The degree of closure regulates the flow of air and fuel into the engineand therefore the speed with which the engine will run. Engine speed isthus principally dependent upon and regulated by the position of thestopthrottle. The engine will produce less power the more nearly thestop-throttle approaches the position shown in the solid lines.Accordingly, to the extent the engine can overcome a load, the enginewill run at a higher speed as the stop-throttle is moved more nearly tothe position shown in the broken lines. Regardless of the position ofthe stop-throttle, the reed will continue to vibrate from a variablyopen to a closed position in order to prevent reversion by cyclicallyadmitting the flow of air into the engine and isolating the fueldelivery system from positive pressures developed by the engine.

FIG. 3 is an exploded perspective view illustrating the arrangement ofthe elements comprising the improvement. The body 12 of the carburetoris illustrated in broken lines. The base surface 90 or other suitableseating means of body 12 terminates the upstream portion 74 of the airpassage and provides a base to which the flexible elongated reed 64 canbe secured and a seat against which the reed may snugly rest whenclosed. The reed 64 is bifurcated into identical petals 96 in theembodiment illustrated. The connective base of the reed is secured tothe base surface 90 of body 12 by means of a formed backup clamp 68 andthreaded fasteners 66 which thread into the apertures 92. The reed clamp68 is flat in the area used to secure the reed to surface 90. The clampis formed into a slight radius beginning at crease 98 in order tocontrol the bending stress in the petals 96 of the reed 64. At wide openthrottle the stop-throttle 86 forms an extension of the curvature begunin clamp 68 (see FIG. 2). When the reed 64 is in place on the surface90, dual openings 100 which provide communication between the upstreamand the downstream portions of the air passage are fully and snuglycovered. The tips 70 of the reed fully cover and directly seal the idleports 72. The dual openings 100 are separated by a septum 102 whichextends a distance into the upstream portion 74 of the air intakepassage 16.

The embodiment shown here uses two openings 100 in body 12, and twopetals on reed 64. A carburetor designed to provide less air flow woulduse only one opening 100 in body 12, and a single petal on reed 64.Likewise, a carburetor designed to provide more air flow would use threeopenings covered with three petals in a single body.

The throttle lever, pivot pin, and stop-throttle can be seen at 22, 24,and 86, respectively. As illustrated, the stop throttle is secured tothe pivot pin by inserting an edge 104 of the stop-throttle into alongitudinally extending slot 106 in the pivot pin 24. The stop-throttleis then securely fastened therein by means of threaded fasteners 108which are threaded through the apertures 110 and 1 12. Of course, thoseskilled in the art will appreciate that the stop-throttle could beconnected to the pivot pin by a number of suitable methods. Forinstance, a longitudinal portion of the pivot pin could be machined toprovide a flat abutting surface. The stopthrottle could then be securedagainst this surface by means of threaded fasteners passing through thestopthrottle into the pivot pin.

When in position, the pivot pin 24 rotates in the bearing 114 of thethrottle support plate 26. The entire assembly is enclosed by thethrottle support plate 26 which is secured to the surface by threadedfasteners threaded through the apertures 1 16. The assembled carburetorcan then be secured to the insulating base plate 28 as illustrated inFIG. 1 by threaded fasteners disposed in apertures 1 18 of the throttlesupport plate SUMMARY OF ADVANTAGES It will be appreciated that inproviding an improved carburetor according to the present inventioncertain significant advantages are obtained.

Of particular importance is the advantage that the improved carburetoris more compact and therefore better suited to use in engines employedto power chain saws, motorcycles, and other devices in which littlespace is available for the reed valve and carburetor on the engine.

Also quite important is the advantage gained by the removal of arestrictive venturi and throttle shaft in the air passage upstream fromthe reed. The resulting uncluttered air passage will permit more air toflow to the engine, giving better peak engine power.

At lower engine speeds, the reed carburetor provides the advantage of avariable venturi which ensures an adequate velocity head for effectiveaspiration of fuel from the fuel ports when the engine is operated bothat full throttle and at low speed. The variable venturi created beneaththe reed petal adds to the lugging ability of the engine at low speed,in spite of the decreased volume of air required by the engine.

Also quite important is the improvement in which the main and idlingfuel ports are positioned in very close proximity to one another and tothe center of the fuel reservoir so that the static fuel head willremain essentially equal for both ports regardless of the position ofthe carburetor.

Furthermore, the unique provision of a venturi for the aspiration offuel from an idling fuel port provides the important advantage ofensuring efficient atomization of the fuel into a mixture which can beeffectively inducted into the engine when the engine is idling.

A still further advantage resides in the improvement in which the reedsare moved from a position of very close proximity with the crankcase toa position within the carburetor in which they are exposed to less heatand air turbulence.

In describing the invention, reference has been made to a preferredembodiment. However, those skilled in the art and familiar with thedisclosure of the invention may recognize additions, deletions,substitutions, or

13 other modifications which would fall within the perview of theinvention as defined in thelclaims.

What is claimed is: w I l. A method of carbureting fuel and aircomprising: providing induction passage means having an air receivinginlet and a fuel and air discharging outlet; providing fuel supplyingorifice means communicating with said induction passage means andoperable to discharge fuel thereinto; providing flexible reed valvemeans extending transversely across said induction passage means, saidflexible reed valve means being concurrently operable to throttle theflow of air through said induction passage means in response tooperation of engine throttle control means, prevent a reverse flow ofair through said induction passage means from the outlet thereof towardthe inlet thereof, and induce aspiration of fuel from said fuelsupplying orifice means into said induction passage means; providingthrottle linkage means connected with said engine throttle controlmeans; providing and deploying throttle movement limiting means todefine selectively variable throttling positions of said flexible reedvalve means with respect to said induction passage means and said fuelsupplying orifice means; and manipulating said throttle movementlimiting means on said throttle linkage means to cause said throttlingaction of said flexible reed valve means, as determined by selectivepositioning of said throttle movement limiting means, to be responsiveto operation of said engine throttle control means. 2. A carburetorapparatus operable to supply air and fuel to engine means andcomprising:

induction passage means having an air receiving inlet and a fuel and airdischarging outlet; fuel supplying orifice means communicating with saidinduction passage means and operable to discharge fuel thereinto;flexible reed valve means extending transversely across said inductionpassage means, said flexible reed valve means being concurrentlyoperable to throttle the flow of air through said induction passagemeans in response to operation of engine throttle control means, preventa reverse flow of air through said induction passage means from theoutlet thereof toward the inlet thereof, and induce aspiration of fuelfrom said fuel supplying orifice means into said induction passagemeans; throttle linkage means operable to be connected with said enginethrottle control means; throttle movement limiting means operable todefine selectively variable throttling positions of said flexible reedvalve means with respect to said induction passage means and said fuelsupplying orifice means; and means mounting said throttle movementlimiting means on said throttle linkage means to cause said throttlingaction of said flexible reed valve means, as determined by selectivepositioning of said throttle movement limiting means, to be responsiveto operation of said engine throttle control means.

14 3. A carburetor apparatus as described in claim 2, wherein:

said flexible reed valve means is operable to provide a freely movable,outer end portion projecting beyond said throttle movement limitingmeans,

said outer end portion of said flexible reed valve means is operable toundergo flexing movement beyond said throttle movement limiting meanswhile an anchored, innerendportion of said flexible reed valve means isengaged with said throttle movement limiting means at relatively lowerspeeds of said engine means so as to permit induction passage opening,flexing movement of said freely moveable outer end portion of saidflexible reed valve means operable to induce aspiration of fuel intosuch induction passage means from said fuel supplying orifice means atsaid relatively lower speeds of said engine means, while said inner endportion is restrained by said throttle movement limiting means; and

said flexible reed valve means is operable, at relatively higher speedsof said engine means, to undergo flexing movement of both said inner andouter portions, with said flexing of said inner and outer portions ofsaid flexible reed valve means being operable to induce aspiration offuel into said induction passage means through said fuel supplyingorifice means.

4. A carburetor apparatus as described in claim 3 including:

check valve means included in said fuel supplying orifice means andoperable to prevent a flow of air from said induction passage meansthrough said fuel supplying orifice means associated with said checkvalve means.

5. In a carburetorsfor mixing and introducing fuel and air into aninternal combustion engine, said carbureto including;

an air intake port for admitting air into said carburetor,

an air passage through which air may be conducted from said intake portto said internal combustion engine,

a fuel inlet for admitting fuel into said carburetor,

idle and main fuel orifice means opening into said air passage forintroducing fuel into said air passage, and

idle and main fuel circuit means, connected to said fuel inlet andfurther connected with said air pas-' sage through said orifice means,for conducting fuel from said fuel inlet to said air passage wherein airand fuel are mixed and from which the mixture is introduced into saidinternal combustion engine, an improvement which comprises:

flexible elongated means, within and connected to said carburetor, foradmitting air and fuel to said engine and for preventing exposure tosaid orifice means to back pressure developed by said engine, saidflexible elongated means being disposed in a cantilevered posture acrosssaid air passage to normally cover said passage and being movable to avariably open position by air passing through said passage;

regulating means, connected to said carburetor and operably associatedwith said flexible elongated means, for selectively engaging andreleasing said flexible elongated means to regulate the quantity of airand fuel entering said engine; and

seating means, disposed in said air passage, for seating said flexibleelongated means to isolate air within said passage upstream of saidseating means from air within said passage downstream of said seatingmeans, said seating means having an opening for the passage of airtherethrough and surface means adjacent thereto for forming a variableventuri with the free end of said flexible elongated means when saidflexible elongated means is in said variably open position in responseto the flow of air through said air passage; said idle and main fuelorifice means being positioned relative to said free end of saidflexible elongated means with sufficient proximity to cause aspirationof fuel from said orifices by air passing through said variable venturi;said seating means including a transverse member disposed across saidair passage having dual openings therein through which air can pass froman upstream portion of said air passage to a downstream portion, and aseptum means connected to said transverse member, said septum meansbeing oriented to 16 extend generally longitudinally of said airpassage, transversely intersect said planar member, and divide said airpassage adjacent said transverse member into dual channels. 6. Animproved carburetor, for mixing and introducing fuel and air into aninternal combustion engine, as defined in claim 5 wherein said flexibleelongated means comprises:

a bifurcated reed having elongated petals for covering said dualopenings. 7. An improved carburetor, for mixing and introducing fuelandair into an internal combustion engine, as defined in claim 5 whereinsaid regulating means comprises:

contact means for contacting each of said elongated petals of saidbifurcated reed, across the width thereof, to selectively close saidbifurcated reed to regulate the quantity of air and fuel entering saidengine, said regulating means clamping said elongated petals againstsaid seating means when said regulating means is in a position of fullclosure.

1. A method of carbureting fuel and air comprising: providing inductionpassage means having an air receiving inlet and a fuel and airdischarging outlet; providIng fuel supplying orifice means communicatingwith said induction passage means and operable to discharge fuelthereinto; providing flexible reed valve means extending transverselyacross said induction passage means, said flexible reed valve meansbeing concurrently operable to throttle the flow of air through saidinduction passage means in response to operation of engine throttlecontrol means, prevent a reverse flow of air through said inductionpassage means from the outlet thereof toward the inlet thereof, andinduce aspiration of fuel from said fuel supplying orifice means intosaid induction passage means; providing throttle linkage means connectedwith said engine throttle control means; providing and deployingthrottle movement limiting means to define selectively variablethrottling positions of said flexible reed valve means with respect tosaid induction passage means and said fuel supplying orifice means; andmanipulating said throttle movement limiting means on said throttlelinkage means to cause said throttling action of said flexible reedvalve means, as determined by selective positioning of said throttlemovement limiting means, to be responsive to operation of said enginethrottle control means.
 1. A CARBURETOR APPRATUS OPERABLE TO SUPPLY AIRAND FUEL TO ENGINE MEANS AND COMPRISING: INDUCTION PASSAGE MEANS HAVINGAN AIR RECEIVING INLET AND A FUEL AND AIR DISCHARGING OUTLET, FUELSUPPLYING ORIFICE MEANS COMMUNICATING WITH SAID INDUCTION PASSAGE MEANSAND OPERABLE TO DISCHARGE FUEL THEREINTO, FLEXIBLE REED VALVE MEANSEXTENDING TRANSVERSELY ACROSS SAID INDUCTION PASSAGE MEANS SAID FLEXIBLEREED VALVE MEANS BEING CONCURRENTLY OPERABLE TO THROTTLE THE FLOW OF AIRTHROUGH SAID INDUCTION PASSAGE MEANS IN RESPONSE TO OPERATION OF ENGINETHROTTLE CONTROL MEANS, PREVENT A REVERSE FLOW OF AIR THROUGH SAIDINDUCTION PASSAGE MEANS FROM THE OUTLET THEREOF TOWARD THE INLET THEREOFAND INDUCE ASPIRATION OF FUEL FROM SAID FUEL SUPPLYING ORIFICE MEANSINTO SAID INDUCTION PASSAGE MEANS, THROTTLE LINKAGE MEANS OPERABLE TO BECONNECTED WITH SAID ENGINE THROTTLE CONTROL MEANS, THROTTLE MOVEMENTLIMITING MEANS OPERABLE TO DEFINE SELECTIVELY VARIABLE THROTTLINGPOSITIONS OF SAID FLEXIBLE REED VALVE MEANS WITH RESPECT TO SAIDINDUCTION PASSAGE MEANS AND SAID FUEL SUPPLYING ORIFICE MEANS AND MEANSMOUNTING SAID THROTTLE MOVEMENT LIMITING MEANS ON SAID THROTTLE LINKAGEMEANS TO CAUSE SAID THROTTLING ACTION OF SAID FLEXIBLE REED VALVE MEANSAS DETERMINED BY SELECTIVE POSITIONING OF SAID THROTTLE MOVEMENTLIMITING MEANS, TO BE RESPONSIVE TO OPERATION OF SAID ENGINE THROTTLECONTROL MEANS.
 3. A carburetor apparatus as described in claim 2,wherein: said flexible reed valve means is operable to provide a freelymovable, outer end portion projecting beyond said throttle movementlimiting means, said outer end portion of said flexible reed valve meansis operable to undergo flexing movement beyond said throttle movementlimiting means while an anchored, inner end portion of said flexiblereed valve means is engaged with said throttle movement limiting meansat relatively lower speeds of said engine means so as to permitinduction passage opening, flexing movement of said freely moveableouter end portion of said flexible reed valve means operable to induceaspiration of fuel into such induction passage means from said fuelsupplying orifice means at said relatively lower speeds of said enginemeans, while said inner end portion is restrained by said throttlemovement limiting means; and said flexible reed valve means is operable,at relatively higher speeds of said engine means, to undergo flexingmovement of both said inner and outer portions, with said flexing ofsaid inner and outer portions of said flexible reed valve means beingoperable to induce aspiration of fuel into said induction passage meansthrough said fuel supplying orifice means.
 4. A carbUretor apparatus asdescribed in claim 3 including: check valve means included in said fuelsupplying orifice means and operable to prevent a flow of air from saidinduction passage means through said fuel supplying orifice meansassociated with said check valve means.
 5. In a carburetor for mixingand introducing fuel and air into an internal combustion engine, saidcarburetor including; an air intake port for admitting air into saidcarburetor, an air passage through which air may be conducted from saidintake port to said internal combustion engine, a fuel inlet foradmitting fuel into said carburetor, idle and main fuel orifice meansopening into said air passage for introducing fuel into said airpassage, and idle and main fuel circuit means, connected to said fuelinlet and further connected with said air passage through said orificemeans, for conducting fuel from said fuel inlet to said air passagewherein air and fuel are mixed and from which the mixture is introducedinto said internal combustion engine, an improvement which comprises:flexible elongated means, within and connected to said carburetor, foradmitting air and fuel to said engine and for preventing exposure tosaid orifice means to back pressure developed by said engine, saidflexible elongated means being disposed in a cantilevered posture acrosssaid air passage to normally cover said passage and being movable to avariably open position by air passing through said passage; regulatingmeans, connected to said carburetor and operably associated with saidflexible elongated means, for selectively engaging and releasing saidflexible elongated means to regulate the quantity of air and fuelentering said engine; and seating means, disposed in said air passage,for seating said flexible elongated means to isolate air within saidpassage upstream of said seating means from air within said passagedownstream of said seating means, said seating means having an openingfor the passage of air therethrough and surface means adjacent theretofor forming a variable venturi with the free end of said flexibleelongated means when said flexible elongated means is in said variablyopen position in response to the flow of air through said air passage;said idle and main fuel orifice means being positioned relative to saidfree end of said flexible elongated means with sufficient proximity tocause aspiration of fuel from said orifices by air passing through saidvariable venturi; said seating means including a transverse memberdisposed across said air passage having dual openings therein throughwhich air can pass from an upstream portion of said air passage to adownstream portion, and a septum means connected to said transversemember, said septum means being oriented to extend generallylongitudinally of said air passage, transversely intersect said planarmember, and divide said air passage adjacent said transverse member intodual channels.
 6. An improved carburetor, for mixing and introducingfuel and air into an internal combustion engine, as defined in claim 5wherein said flexible elongated means comprises: a bifurcated reedhaving elongated petals for covering said dual openings.
 7. An improvedcarburetor, for mixing and introducing fuel and air into an internalcombustion engine, as defined in claim 5 wherein said regulating meanscomprises: contact means for contacting each of said elongated petals ofsaid bifurcated reed, across the width thereof, to selectively closesaid bifurcated reed to regulate the quantity of air and fuel enteringsaid engine, said regulating means clamping said elongated petalsagainst said seating means when said regulating means is in a positionof full closure.